The present invention relates to a thick film resistor comprising a resistive film element and electrodes which are partly overlapped on each other and more particularly to a thick film resistor in which the residual resistance and contact noise of the overlapped portion of the resistive film element and the electrode are significantly reduced.
Referring to FIG. 1, there is schematically shown a conventional thick film horseshoe-shaped variable resistor. In the figure, reference numeral 1 represents an insulating substrate, reference numeral 2 terminal electrodes and reference numeral 3 a resistive film element. This type of thick film resistor has the shortcomings that the electric resistance (residual resistance) of the overlapped portions 4,4 of the resistive film element 3 and the electrodes 2,2 is much greater than that of the other portions of the resistive film element and that great contact noise is generated from the overlapped portions 4,4. These shortcoming are particularly marked when electrode 2 is formed by using a conductive material containing much Ag. Usually, in such terminal electrode 2, Ag, Ag-Pd or Ag-Pt electrodes containing a great amount of Ag are most commonly used since they are excellent in solderability and electric conductivity and comparatively low in cost. However, the above-mentioned shortcomings, such as great residual resistance and generation of contact noise are unavoidable.
Therefore, when using this sort of thick film resistor, a movable contact is stopped immediately before the overlapped portion 4 of the electrode 2 and the resistive film element 3. In this method, however, the resistive film element 3 cannot be used to the upper and lower limits of its intrinsic resistance and, consequently, its resistance-adjustable range is reduced, so that it is difficult to utilize its characteristics sufficiently. In particular, it is difficult to minimize its resistance to near zero although it is important for variable resistors to be capable of reducing the resistance to zero as much as possible.
Referring to FIG. 2, there is schematically shown a resistor network comprising multiple resistive film elements 3 having different aspect ratios (i.e. the ratio of the length to the width), which are formed on the insulating substrate 1. In the resistor network, resistance of each resistive film element is found to be deviated greatly from the resistance pre-estimated from its geometrical shape due to the generation of the residual resistance in the overlapped portions of the resistive film elements 3 and the electrodes 2. Furthermore, since its deviation is irregular, the properties of the produced resistor are not uniform. This may bring about much difficulty in performing the circuit design.